1. Field of the Invention
The present invention relates to a zoom lens system, an imaging device and a camera. In particular, the present invention relates to: a zoom lens system that has a remarkably reduced thickness at the time of accommodation so as to be suitable for a lens barrel of so-called retraction type and that is still provided with a wide view angle at a wide-angle limit and with a zooming ratio exceeding 3.2; an imaging device employing this zoom lens system; and a thin and compact camera employing this imaging device.
2. Description of the Background Art
Remarkably strong demands are present for size reduction of cameras such as digital still cameras and digital video cameras (simply referred to as digital cameras, hereinafter) provided with an image sensor for performing photoelectric conversion. In particular, in digital cameras provided with a zoom lens system having a zooming ratio of 3 or the like, which are most frequent in the number of sales in the market, popularity goes to a construction of external structure in which at the time of accommodation (at the time of non-image taking), the overall length of the lens barrel is reduced (lens barrel is retracted) so that the lens barrel itself does not protrude outside. Further, in recent years, zoom lens systems are also desired that have a wide angle range where the image taking field is large.
As zoom lens systems suitable for the above-mentioned digital cameras, for example, the following zoom lens systems are proposed.
For example, Japanese Laid-Open Patent Publication No. 2005-331860 discloses a variable magnification optical system, in order from the object side, including a first lens unit having negative optical power and a second lens unit having positive optical power, wherein: at the time of magnification change from a wide-angle limit to a telephoto limit, the interval between the first and the second lens units is reduced; the first lens unit is composed of two or more lenses; and at least three lens units are each composed solely of a single lens or a cemented lens.
Japanese Laid-Open Patent Publication No. 2006-011096 discloses a variable magnification optical system, in order from the object side, including a first lens unit having negative optical power and a second lens unit having positive optical power each composed of a plurality of lenses, wherein: at the time of magnification change from a wide-angle limit to a telephoto limit, the interval between the first and the second lens units is reduced; the first lens unit has at least one aspheric surface; and a predetermined condition is satisfied by all of the maximum of the refractive index difference (absolute value) of the two lenses in the first lens unit, the composite focal length of the second lens unit, and the optical axial distance from the surface vertex of the most-image-sensor-side lens surface to the image sensor surface at a telephoto limit.
Japanese Laid-Open Patent Publication No. 2006-023679 discloses a zoom lens, in order from the object side to the image side, comprising a first lens unit having negative refractive power and a second lens unit having positive refractive power, wherein: the interval between the two lens units varies during the zooming; the first lens unit comprises a lens 11 having negative refractive power and a lens 12 having positive refractive power; the second lens unit comprises a lens 21 having positive refractive power and a lens 22 having negative refractive power; and the Abbe numbers of the lens 21 and the lens 22 satisfy a predetermined condition.
Japanese Laid-Open Patent Publication No. 2006-065034 discloses a zoom lens, in order from the object side to the image side, comprising a first lens unit having negative refractive power, a second lens unit having positive refractive power and a third lens unit having positive refractive power, wherein: the intervals between the individual lens units vary during the zooming; the first lens unit is composed of one negative lens and one positive lens; the second lens unit comprises a second-a lens unit composed of one positive lens and one negative lens and a second-b lens unit that is arranged on the image side of the second-a lens unit and that has at least one positive lens; the third lens unit has at least one positive lens; and a predetermined condition is satisfied by the image magnifications at a wide-angle limit and a telephoto limit of the second lens unit, the interval between the first and the second lens units at a wide-angle limit, and the interval between the second and the third lens units at a telephoto limit.
Japanese Laid-Open Patent Publication No. 2006-084829 discloses a zoom lens, in order from the object side to the image side, comprising a first lens unit having negative refractive power, a second lens unit having positive refractive power and a third lens unit having positive refractive power, wherein: the intervals between the individual lens units vary during the zooming; the second lens unit comprises a second-a lens unit composed of, in order from the object side to the image side, a positive lens and a negative lens and a second-b lens unit that is arranged on the image side of the second-a lens unit and that has at least one positive lens; and a predetermined condition is satisfied by the half view angle at a wide-angle limit, the focal lengths of the first and the second lens units and the focal length of the entire system at a wide-angle limit.
Japanese Laid-Open Patent Publication No. 2006-139187 discloses a zoom lens, in order from the object side, comprising a first lens unit having negative refractive power, a second lens unit having positive refractive power and a third lens unit having positive refractive power, wherein: the intervals between the individual lens units are changed so that variable magnification is achieved; the second lens unit is composed of two lens components consisting of a single lens on the object side and a lens component on the image side; and a predetermined condition is satisfied by the radii of curvature of the single lens on the object side and the image side and the lens optical axial thickness of the single lens.
Japanese Laid-Open Patent Publication No. 2006-171421 discloses a zoom lens, in order from the object side to the image side, comprising a first lens unit having negative refractive power, a second lens unit having positive refractive power and a third lens unit having positive refractive power, wherein: the intervals between the individual lens units vary during the zooming; the first lens unit, in order from the object side to the image side, comprises one negative lens and one positive lens; the second lens unit, in order from the object side to the image side, comprises a positive lens, a positive lens, a negative lens and a positive lens; and during the zooming from a wide-angle limit to a telephoto limit, the third lens unit moves to the image side.
Japanese Laid-Open Patent Publication No. 2006-208890 discloses a zoom lens, in order from the object side to the image side, comprising a first lens unit having negative refractive power, a second lens unit having positive refractive power and a third lens unit having positive refractive power, wherein: the intervals between the individual lens units vary during the zooming; and a predetermined condition is satisfied by the amount of movement of the second lens unit during the zooming from a wide-angle limit to a telephoto limit, the interval between the second and the third lens units at a wide-angle limit, the focal lengths of the first and the second lens units and the focal length of the entire system at a wide-angle limit.
Japanese Laid-Open Patent Publication No. 2006-350027 discloses a zoom lens, in order from the object side, comprising at least a first lens unit composed of two components and a second lens unit composed of one component, wherein: at the time of magnification change, at least the interval between the first and the second lens units varies; the first and the second lens units have aspheric surfaces; and a predetermined condition is satisfied by the paraxial radius of curvature of at least one aspheric surface A of the first lens unit and the distance between the intersecting point where the most off-axis principal ray passes through the aspheric surface A and the optical axis.
Japanese Laid-Open Patent Publication No. 2006-194974 discloses a zoom lens, in order from the object side to the image side, comprising a first lens unit having negative refractive power and a second lens unit having positive refractive power, wherein: the interval between the individual units is changed so that magnification change from a wide-angle limit to a telephoto limit is achieved; the first lens unit is, in order from the object side, composed of two lenses consisting of a negative lens and a positive lens; and a predetermined condition is satisfied by the Abbe number of the positive lens, the refractive index of the positive lens and the refractive index of the negative lens.
Japanese Laid-Open Patent Publication No. 2006-220715 discloses a zoom lens, in order from the object side, comprising a first lens unit having negative refractive power, a second lens unit having positive refractive power and a third lens unit having positive refractive power, wherein: the intervals between the individual lens units are changed so that variable magnification is achieved; the first lens unit is composed of two lenses consisting of a negative lens and a positive lens; the second lens unit comprises two positive lenses and one negative lens; the third lens unit is composed of one positive lens; and a predetermined condition is satisfied by the refractive index of the negative lens and the refractive index of the positive lens in the first lens unit.
The optical systems disclosed in the above-mentioned publications have zooming ratios sufficient for application to digital cameras. Nevertheless, width of the view angle at a wide-angle limit and size reduction are not simultaneously realized. In particular, from the viewpoint of size reduction, requirements in digital cameras of recent years are not satisfied.